By Lorenza Brascia and Catherine E. Shoichet CNN

(CNN) -- Investigators trying to piece together what caused EgyptAir Flight 804 to plunge into the Mediterranean Sea now have another clue.

The plane's cockpit voice recorder indicates there was a fire on the aircraft before it crashed -- and an attempt to put it out, a senior source from the airline told CNN Tuesday.

The revelation adds another detail to a picture that's been slowly emerging since the May 19 crash. But investigators have said it's still too soon to say what happened aboard the flight.

The cockpit voice recorder captures sounds from the flight deck, including flight crew conversation, alarms and background noise that can help investigators understand what the flight crew was doing.

Authorities haven't released a transcript or revealed details about what can be heard in the recording. French investigators were working to repair the voice recorder's damaged memory chip.

"What they are not saying, and they are not telling us or discussing, is what might have caused the fire?" CNN aviation correspondent Richard Quest said. "And that remains, of course, the absolute top question."

New data in line with other clues

The source who spoke with CNN Tuesday confirmed the data from the cockpit voice recorder lines up with other data obtained from the flight.

So far, here's what other data has revealed:

• There could have been smoke in a lavatory and in the plane's avionics, according to the flight data recorder.

• The wreckage from the plane's front section showed "signs of high temperature damage and soot," Egypt's civil aviation ministry said.

• There were smoke alerts near the plane's cockpit minutes before it crashed, according to the Aircraft Communications Addressing and Reporting System, a data link for sending messages between planes and ground facilities.

"We now know there was smoke and there was fire onboard at the front of the aircraft. ... We don't know what caused it," Quest said. "And we don't know whether it was avionics-related, mechanical, or -- since it was by the toilet -- had it been done by somebody."

Tied to terror?

The plane crashed May 19 with 56 passengers and 10 crew members aboard.

Speculation quickly swirled over whether terrorism was to blame -- a topic that even became a flashpoint on the U.S. presidential campaign trail.

Egyptian officials have said a terror attack or technical failures could have downed the plane.

CNN's Amy La Porte contributed to this report.

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